The present invention relates generally to telecommunication networks, and more particularly, to a system and method for transmitting data through a wired communication channel using an encoding modem and a decoding modem.
In the modern telecommunication industry, improved technologies for transmitting information through an efficient medium are always needed. Technologies for fast data transmission keep evolving at a rapid pace. For the wired world, modems are still one of the key instruments for users to exchange information in a computer network. However, modems in general suffer from numerous delays. For example, current dial-up modems are limited to a speed of about 56 kb/s using data compression technology. Moreover, in order not to sacrifice the accuracy of the information being transmitted, a Forward Error Correction Code (FECC) technique must be implemented to embed sufficient redundant information in the transmitted data, thereby reducing the overall data bandwidth. For an Asymmetric Digital Subscriber Line (ADSL) modem, the current technology provides a transmission speed about 1.5 Mb/s for up stream data flow, and up to 9 Mb/s for down stream data flow. But it is with the assistance of a more complex data compression technology, which increases packet loss rate, and thus in turn damages the integrity of the data transmitted.
For the wireless world, Code Division Multiple Access technology has proved to be a leading communication technology for voice data transmission. One advantage of CDMA technology is that multiple users can share a common frequency without having significant interference. The core technology providing this leading edge is an orthogonal coding technique. In essence, each user is assigned a unique orthogonal code, which enables the user to remain unaffected by other users of the same frequency. However, there is one restrictionxe2x80x94all users using the same frequency must be synchronized in time to the accuracy of a fraction of one bit of an orthogonal code. Otherwise, a desired zero cross-correlation property of orthogonal codes will be lost.
In order to meet this synchronization requirement, a unique pilot signal is utilized to synchronize all users. Even so, it is still difficult to maintain perfect synchronization in multi-path environments since multi-path components are, by their very nature, unpredictable. As a result, the number of CDMA users (N) can be represented by the following capacity equation:                     N        ⁢                  xe2x80x83                ⁢        ∞        ⁢                  xe2x80x83                ⁢                              W            /                          R              b                                                          E              b                        /                          N              o                                                          (        1        )            
where W=Total Available Bandwidth, Rb=bit rate, Eb=Energy/bit, No=Noise spectral density. The ratio W/Rb is known as the xe2x80x9cprocess gain,xe2x80x9d and the ratio Eb/No. is expressed in decibel. Since it is highly desirable to minimize Eb/No so that CDMA capacity can be enhanced, various techniques have been deployed. Notwithstanding these techniques, the system capacity provided by CDMA technology is still significantly impacted by the fact that it is practically impossible to eliminate multi-path components from a wireless environment.
However, this detrimental impact does not exist in a wired environment where multi-path components are negligibly small or practically absent. Therefore, what is needed is a communication application based on CDMA technology for providing fast data transfer in a wired environment.
In the present invention, a system and method for data communication using modems is disclosed. In one embodiment, the system includes an encoding modem where an input binary data stream is split into several parallel sub streams. These parallel sub streams are mapped into a set of unique orthogonal short-codes and then modulated by a bank of modulators, and thereafter, combined and transmitted through a wired communication channel such as cable or optical fiber. Since there are no multipath components in the wired communication channel, the composite outgoing data stream remains orthogonal during the transmission, thus maximizing transmission capacity.
By implementing the present invention, a dial-up modem using CDMA technology can offer a speed of at least 128 kb/s without data compression and with a far less complicated FECC process. Similarly, an ADSL modem using CDMA technology can offer a speed of at least 18 Mb/s without data compression.
The system may also include a decoding modem that can easily decode information encoded and transmitted by the encoding modem.